Configuring Hardware and Communication Connections STEP 7.pdf

Configuring the Distributed I/O (DP)
The period starting at the point when an input is detected at the electronic module
to the reaction at an output results in a constant processing time of Ti + TDP +
To. This condition ensures a constant process reaction time described by: TDP +
Ti + TDP + To.
Prerequisites and General Conditions
• H-systems (redundant/fault-tolerant) do not support cycle synchronization.
• In F-systems, cycle synchronization cannot be used for non-failsafe I/O
devices/peripherals.
• Cycle synchronization cannot be used on optical PROFIBUS networks.
• Constant bus cycle time and cycle synchronization are only possible with the
"DP" and "User-defined" bus profiles. However, using the "User-defined" profile
is not recommended.
• Cycle synchronization is only possible with DP interfaces integrated in the CPU.
• At a cycle-synchronized PROFIBUS-DP, only the constant-bus-cycle-time
master can be the active station. OPs and programming devices(PG) (or PCs
with PG functionality) influence the timing of the constant-bus-cycle-time DPcycle.
For this reason, they are not recommended.
• Cycle synchronization among chains is not possible at this time.
• Cycle-synchronized I/O devices can only be processed in process image
partitions (part process images). Process image partitions are required to
achieve consistent, cycle-synchronized data transmission. Without them,
consistent, cycle-synchronized data transmission is not possible. To ensure that
a process image partition remains consistent, STEP 7 monitors the quantity of
data (the number of slaves and number of bytes per process image partition for
the DP master system are limited). In addition, please observe the following
points:
- Within a station, input addresses must not be assigned to different process
image partitions.
- Within a station, output addresses must not be assigned to different
process image partitions.
- A common process image partition can be used for both input and output
addresses.
• In HW Config, the address of the cycle-synchronized analog I/O devices must
be located in the address area of the process image partition.
• Cycle synchronization is only possible with ET 200M and ET 200S devices;
synchronization with centralized I/O devices is not possible.
• Full cycle synchronization "from terminal to terminal" is only possible if all
components in the chain support the "Isochrone mode" system property. When
selecting devices in a catalog or in the hardware catalog, make sure that the
information field for the modules contains the entry "Isochrone mode". The
latest updated list is available in the Internet at
http://www.ad.siemens.de/support, Entry ID 14747353.
Configuring Hardware and Communication Connections with STEP 7
3-86 A5E00706939-01